The present invention relates to multi-station packet communication in which a single transmit station sends the same message to a plurality of receive stations and, more particularly, to a packet repeat request signal transmitting method for a network in which all the receive stations connected to a radio link or a bus type wire link are capable of observing information which is being transmitted over the link.
Multi-station communication in a radio link, a bus type wire link and other networks has the outstanding capability for delivering information to all the receive stations in the network by a single communication because all the receive stations are capable of observing the same information. However, the problem with multi-station communication is that when a plurality of receive stations respond with repeat requests, or retransmission requests, at the same time due to transmission errors, the repeat request signals conflict with each other in the link. As a result, repeat requests cannot be correctly sent back to a transmit station.
The occurrence of a conflict particular to a situation wherein a plurality of receive stations share the same communication link is well known in the art as a problem with multi-access.
Multi-access systems may generally be classified into two types, i.e., a transmission right control system which sequentially assigns a transmission right to all the receive stations, and a random access type which in the event of a conflict detects it and retransmits information after a suitable delay time. Although the transmission right control type system is free from conflicts, it needs to exchange some information for controlling the repeat request signal returning timings among receive stations, resulting in a complicated control. An example of retransmission protocol of this kind is disclosed in S. B. Calo and M. C. Easton "A Broadcast Protocol for File Transfers to Multiple Sites", IEEE Transactions of Communications, Vol. COM-29, No. 11, November 1981, pages 1701-1707. The technique disclosed in this paper is such that a transmit station sends N packets and each transmit station sends an ACK frame back to the transmit station to report whether it successfully received the N packets without error (CYCLE 1) and, thereafter, the transmit station retransmits packets based on the returned ACK frames (CYCLE 2). Such a procedure is repeated until all the packets have been transmitted. This ACK frame scheme, however, brings about another problem that a disproportionate period of time is necessary for all the packets to be successfully transmitted. Also, the time necessary for transmitting a repeat request signal becomes considerably long if the number of receive stations is great. In addition, since receive stations for which a multi-station communication is meant are usually changed at each communication, the control over the returning timings among the receive stations becomes further complicated. The random access type system, on the other hand, involves a considerable probability of conflict which limits the efficiency, because repeat request signals in most cases are generated at the same time by a plurality of receive stations.